JP7338874B2 - magnetic clamping device - Google Patents

Description

The present invention relates to a magnetic clamping device that detects changes in the state of magnetic attraction while a mold is magnetically attracted to an injection molding machine.

2. Description of the Related Art A magnetic clamping device that utilizes a magnetic attracting force is known for fixing a mold of an injection molding machine. A magnetic clamping device is a technology that attaches a magnetic plate to a platen to magnetically fix a mold. The plate has a magnet whose polarity cannot be reversed and a magnet whose polarity is reversible (alnico magnet). By controlling the magnetic polarity of the alnico magnet with a coil, a magnetic circuit closed in the plate and a magnetic It is possible to switch between the circuits.

In order for the mold to be magnetically attracted to the plate, the magnetic clamps must magnetize the mold sufficiently. However, in practice there are many factors that reduce the magnetic flux between the magnetic clamping device and the mold. For example, an external force exceeding the magnetic adsorption force acts on the mold due to overpacking that pressurizes the mold too much, misuse of an ejector rod, ejection by a nozzle, or the like. As a result, the mold falls from the magnetic clamping device.

According to Patent Document 1, a plurality of magnetic attraction units for fixing a mold and detection means for detecting the operating state of the magnetic clamping device are provided. The probe coil of this detection means is mounted outside the main coil of the magnetic attraction unit. As a result, when the mold moves slightly with respect to the magnetic clamping device, a voltage is induced in the search coil and an abnormality in the magnetized state is detected.

The induced voltage is a function of the number of turns multiplied by the rate of change of flux: small flux changes in short time intervals produce large voltages. According to Patent Document 2, a technique is known in which a coil for switching the polarity of an alnico magnet is also effectively used as a detection coil for detecting misalignment or floating of a mold. By increasing the number of turns of the coil, a weak magnetic flux change is detected to generate an induced electromotive force that is higher than the noise.

Further, in Patent Document 3, when the voltage waveform induced in the coil continues for a predetermined time than the first threshold value, or when the voltage exceeds the second threshold value exceeding the first threshold value even for a short period of time Disclosed is a method for judging an abnormality when it occurs.

Japanese translation of PCT publication No. 2005-515080 Japanese Patent No. 5385544 Japanese Patent No. 5683826

In Patent Literatures 1, 2, and 3, an induced voltage generated in a coil is measured, and when it exceeds a threshold value set in a comparison circuit, an emergency is generated assuming that the mold is displaced or lifted. The threshold is set to such an extent that malfunction due to noise does not occur. In Japanese Patent Laid-Open No. 2002-200010, pulse-like fluctuations are judged to be abnormal based on the second threshold, and fluctuations in which the induced voltage continues for a predetermined period of time are judged to be abnormal based on the first threshold, which is smaller than the second threshold.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic clamping device capable of more finely measuring the induced voltage generated in the coil and selecting various countermeasures against the decrease in the magnetizing force.

In the present invention, a reversible magnet capable of reversing the polarity and a non-reversible magnet having an inner pole on the inner peripheral side are placed on the surface of a plate made of a magnetic material that magnetically clamps the mold in a magnetized state. In a magnetic clamping device in which a large number of a plurality of magnet blocks are arranged,
a coil wound around the reversible magnet or wound around the inner pole to detect transient changes in magnetic flux passing through the reversible magnet; and an induction detected from the coil by the transient changes in magnetic flux. Whether or not the positive and negative polarities of the voltage are reversed is determined by a threshold value of the positive and negative voltages, and when the reversal of the positive and negative polarities of the induced voltage is detected, it is possible to determine that the mold has not moved from the initial position. It is characterized by having a control device that judges that the suction force is slightly detached and the state is about to be peeled off.

According to the present invention, even if the magnetizing force of the magnet block is weakened, if the mold is clamped to the magnet block in the initial position, the mold can be closed and magnetized again, and the magnetization can be performed in a short time. There is an effect that the work can be resumed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a diagram showing an injection molding machine, FIG. 1A is an overall view, and FIGS. 2A is a left side magnet plate and FIG. 2B is a right side magnet plate. FIG. FIG. 5 is a diagram showing a transient state of voltage detected in a coil when the mold moves slightly; It is a figure which shows an Example, FIG. 4A is a block diagram, FIG. 4B is a figure which shows a flow.

Examples of the present invention will be described below.
In FIG. 1A, an injection molding machine 1 includes left and right platens 2 and 3 to which molds M1 and M2 are attached, respectively, and a guide rod 9 that guides and supports the left platen 2 so that it can move forward and backward in the left and right direction. there is Magnetic clamp devices 10 and 20 for magnetically attracting the molds are attached to the platens 2 and 3, respectively. 6 is a nozzle for injecting resin, 7 is a controller with a liquid crystal display screen, and 8 is an ejector rod for pushing out the injection molded product from the mold M1. Further, 4 and 5 are mold auxiliary fittings, respectively.

1B to 1D are diagrams for explaining the procedure for magnetically attracting the left and right molds M1 and M2 to the respective magnetic clamp devices 10 and 20. FIG. The left and right molds M1 and M2 are combined with each other, and suspended between the magnetic clamp devices 10 and 20 (FIG. 1B). At this time, the magnetic clamping devices 10 and 20 are in a state in which the molds M1 and M2 are demagnetized (a demagnetization state in which they are not magnetically attracted). Next, the left platen 2 is moved rightward to sandwich the molds M1 and M2 between the magnetic clamp devices 10 and 20. As shown in FIG. In this state, the magnetic clamping devices 10 and 20 are switched from the demagnetized state to the magnetized state (the magnetized state for magnetically attracting the dies M1 and M2) (FIG. 1C). Next, the wires W suspending the molds M1 and M2 are attached to the mold auxiliary fittings 4 and 5 provided on the respective platens 2 and 3 (Fig. 1D). The reason why the mold auxiliary fittings 4 and 5 are used is to prevent the molds M1 and M2 from dropping to the floor. In the state shown in FIG. 1D, the molds M1 and M2 are magnetically clamped by the magnetic clamping devices 10 and 20 .

FIG. 2 is a top view of the magnetic clamping devices 10 and 20. FIG. 2A is the magnetic clamping device 10 on the left and FIG. 2B is the magnetic clamping device 20 on the right. A large number of magnet blocks 11 and 21 are arranged on the surface of the magnetic clamp devices 10 and 20 . In addition, proximity sensors 12 and 22 and magnetic flux coils (not shown) for detecting changes in magnetic flux are arranged. The magnetic clamp device 10 is provided with a through hole 13 into which the ejector rod 8 is inserted.

The main body of the magnetic clamp device 10 is a plate (made of steel) PL made of a magnetic material, and a large number of circular grooves 14 and 24 are provided on the surface (left side of the drawing). Parts surrounded by the grooves 14 and 24 correspond to the magnet blocks 11 and 21 .

Since the magnet blocks 11 and 21 have the same structure, the magnet block 11 will be described below as a representative. FIG. 2C is a view taken along line XX in FIG. 2A. In the figure, the plate PL is integrally provided with a portion D1 made of thin steel on the inner peripheral side of the groove portion 14, and a disk-shaped inner pole D2 made of thick steel inside the portion D1. ing. A ring-shaped non-reversible magnet 15 is fitted in the portion D1 where the thickness of the steel is reduced from the back side of the plate PL. The non-reversible magnet 15 has magnetic poles on the inner and outer peripheral sides of the ring, which is its outer shape. For example, the inner peripheral side is the S pole and the outer peripheral side is the N pole. A neodymium magnet, for example, can be used as the non-reversible magnet 15 . Arranged behind the non-reversible magnet 15 is a reversible magnet 18 consisting of a disc-shaped alnico magnet 16 and a coil 17 wound around its exterior. A disk-shaped yoke 19 is fitted behind the reversible magnet 18 . The inner peripheral side of the non-reversible magnet 15 is magnetically coupled to the inner pole D2, and is magnetically coupled to the outer peripheral side (outer pole D3) of the portion D1 which is thinner on the outer peripheral side. Alnico magnet 16 is magnetically coupled to inner pole D2 and yoke 19, and yoke 19 is magnetically coupled to outer pole D3. Also, the portion D4 of the groove portion 14 is made thinner than the other portions so as to be easily magnetically saturated. Since the surface side of the plate PL is entirely covered with the rope of the plate PL, the non-reversible magnets 15 and the reversible magnets 18 can be sealed from the working area where the mold M1 is mounted.

FIG. 2D shows the state when the magnetic clamping device 10 is in a demagnetized state. The alnico magnet 16 is a permanent magnet with an N pole on the surface (left side of the drawing) of the plate PL and an S pole on the back side. As a result, the magnetic flux passes through the magnetic circuit composed of the non-reversible magnet 15, the outer pole D3, the yoke 19, the alnico magnet 16 and the inner pole D2. In this state, the magnetic flux does not leak to the surface of the plate PL, and the mold M1 is not attracted.

FIG. 2E shows how the magnetic clamping device 10 is magnetized. By applying a direct current to the coil 17 from the outside, the magnetic poles of the alnico magnet 16 are reversed. The alnico magnet 16 is a permanent magnet with the S pole on the surface of the plate PL and the N pole on the back side. The DC current should be applied only during the time that the polarity of the alnico magnet 16 is reversed and the required magnetic flux is coercive. On the surface side of plate PL, both non-reversible magnet 15 and reversible magnet 18 are coupled as south poles to inner pole D2. With the mold M1 pressed against the surface of the plate PL, these magnetic fluxes pass through the mold M1. As a result, a magnetic circuit composed of the non-reversible magnet 15, the outer pole D3, the mold M1 and the inner pole D2 and a magnetic circuit composed of the alnico magnet 16, the outer pole D3, the mold M1 and the inner pole D2 are formed. is formed. Since the alnico magnet 16 does not have a relatively high coercive force as a permanent magnet, when the mold M1 is lost, the magnetic force of the non-reversible magnet 15 immediately loses the magnetic force directed outward from the surface of the plate PL. will be

FIG. 3 shows the transient state of the induced voltage detected when the alnico magnet 16 is provided with several turns of a coil (sensor coil) and the mold M1 moves slightly. In this example, the relationship between the plate PL and the mold M1 is as shown in FIG. 1D. By colliding the ejector rod 8 against the mold M1, the state in which the mold M1 moves was reproduced. Further, when the proximity sensor 12 detected that the mold M1 was separated from the plate PL by 0.2 mm or more, it was determined that the mold was removed from the plate PL. 3A and 3B are transient waveforms of the induced voltage when the detachment of the mold M1 is detected. In FIG. 3A the ejector rod 8 was struck slowly, and in FIG. 3B it was struck at high speed. Adjusted to achieve the set speed at the time of collision. In both FIGS. 3A and 3B, the ejecting force of the ejector rod 8 is greater than the attracting force of the magnetic clamp device 10. FIG.

FIG. 3A shows a state in which the mold M1 has moved for 200 msec after the collision. Also, FIG. 3B shows a state in which the ejector rod 8 moves abruptly due to the collision and then further shifts.

Next, the ejector rod 8 was caused to collide with the ejector rod 8 in a state in which the force for projecting the ejector rod 8 was smaller than the attraction force of the magnetic clamp device 10 . When the collision speed of the ejector rod 8 was increased and reached a certain speed, the proximity sensor 12 detected mold separation. On the other hand, the voltage waveform shown in FIG. 3C could be observed at the speed at which mold separation was not detected.

According to the waveform of FIG. 3C, mold M1 moves upon impact of ejector rod 8 . At this time, the voltage waveform swings to the negative side, indicating that the magnetic flux passing through the coil is rapidly reduced. After that, the voltage waveform exceeds 0 V and the polarity changes to the positive side (circled portion). It shows that the magnetic flux passing through the coil is increasing. The mold M1 is pulled back and clamped to the plate PL again.

The output voltage e of the coil is
e=-Ndφ/dt
is required. N is the number of turns of the coil.
The magnetic flux Δφ lost due to the behavior of the mold M1 can be evaluated by measuring the voltage induced in the coil. The magnetic flux Δφ can be obtained by integrating the output voltage e over time and dividing it by the number of turns N of the coil.

The separation of the mold M1 is instantaneous. However, at the moment of separation, the alnico magnet 16 is demagnetized because it is given a strong magnetic flux in the opposite direction by the non-reversible magnet 15 . The attracting force of the magnetic clamp device 10 has decreased from the initial state, and the mold M1 is in a state of being slightly peeled off. Also, in FIG. 3C, the lost magnetic flux Δφ is small, but it should be noted that even if the mold M1 is pulled back, the mold M1 may have moved from its initial position.

The flux Δφ lost as described above is the integral of the output voltage e over time divided by the number of coil turns. The negative side is the lost flux and the positive side is the recovered flux. In this embodiment, the voltage induced in the coil is sampled at a specific sampling frequency, and the output voltage e is integrated over time. By preparing a correspondence table for converting this into lost magnetic flux, the total lost magnetic flux Δφ is obtained.

Based on the lost magnetic flux obtained, a warning is given of a decline in the attractive force. Also, if it is determined that the attractive force has decreased several times and it has become difficult to maintain the specified attractive force, a warning may be issued to re-magnetize. Further, when demagnetization is observed, regardless of the calculation result of the magnetic flux, it is assumed that the mold M1 has moved from the initial position, and a warning may be generated.

An embodiment will be described below with reference to FIG. FIG. 4A is a circuit diagram showing the magnetic clamp device 10 as a representative of the left and right magnetic clamp devices 10 and 20. FIG. Since the magnetic clamping device 20 is also the same, the description is omitted.

The magnet block 11 has a coil 17 (magnetizing coil) that magnetizes the alnico magnet 16 and a coil 31 (sensor coil) that detects changes in magnetic flux. Although the coils 31 are provided for all the magnet blocks 11 in the drawing, the coils 31 may be selectively provided for a plurality of magnet blocks 11 . The coil 31 detects the magnetic flux passing through the alnico magnet 16, and is wound around the alnico magnet 16 itself in this embodiment. The coils 31 of each magnet block 11 are connected in series, one end of which is grounded and the other end of which is connected to a voltage dividing circuit 32 . The voltage dividing circuit 32 is a circuit that keeps the induced voltage swinging positively and negatively within the measurable voltage range of the controller. The control device 33 is a microprocessor for control, samples the output voltage of the voltage dividing circuit 32 at a predetermined sampling period (about 1 msec), and stores it in an internal memory. The warning device 36 is, for example, an LED display device or a speaker. Anything that can recognize the type of warning will suffice. Further, the control device 33 may notify a controller (for example, the controller 7 in FIG. 1A) with a higher-level liquid crystal display device of a warning, and the controller side may display the contents of the warning on the liquid crystal screen. In the control device 33, a certain threshold value is set for positive and negative voltages so that noise included in the output of the voltage dividing circuit 32 is not detected.

FIG. 4B shows the program flow of controller 33 . Triggered by the change in the induced voltage, the controller 33 starts sampling (step 40). As a result of sampling, it is determined whether or not there is a change in the induced voltage from negative to positive beyond the 0 level (step 41). If there is no change in the positive induced voltage within a predetermined sampling period (for example, 100 msec), a warning is issued to notify that the clamping state of the mold M1 has changed, including its position (step 43). When the positive and negative polarities have changed, the vanishing magnetic flux is obtained from the table 35 stored in advance in the memory 34 in the control device 33, and the vanishing magnetic fluxes stored in the past are integrated (step 42). If the integrated value does not reach the predetermined threshold value (step 44), a warning is issued that the attracting force has decreased although clamping is in progress (step 45).

If the threshold has been reached, a warning is issued to prompt magnetization again (step 46). In this case, it can be determined that the mold M1 has not moved from its initial position. It is carried out by applying a direct current.

According to this embodiment, even if the magnetic attraction force of the magnet block weakens, if the molds M1 and M2 are clamped to the magnetic clamping device 10 or 20 in their initial positions, the molds M1 and M2 can be held. By closing the door and temporarily switching from the magnetized state to the demagnetized state, the work can be resumed in a short time by re-magnetizing (switching to the magnetized state again).

In step 42 of the present embodiment, when the positive and negative polarities have changed, the vanishing magnetic flux is obtained from the table 35 stored in advance in the memory 34 in the control device 33, and the integrated value must reach a predetermined threshold value. Although it is determined that the mold M1 has not moved from its initial position, a warning may be issued immediately without accumulation. When receiving this warning, the injection molding machine 1 may be stopped, or the magnetic clamping device 10 may be demagnetized once and then magnetized again.

In this embodiment, the output voltage of the voltage dividing circuit 32 is sampled at a predetermined sampling period by the control device 33 and stored in the internal memory. You may memorize|store in internal memory whether it was.

In the above embodiment, the coil 31 (sensor coil) and the coil 17 (magnetizing coil) are separate coils. good. When a magnetic pole reversal coil is used as a sensor coil, a switching circuit is required, but there is the advantage of improved sensitivity. Further, in the above embodiment, the sensor coil 31 wound around the alnico magnet 16 itself is used, but the position of the sensor coil 31 is not limited to that in the present embodiment, and may be arranged at other locations. may For example, it may be arranged so as to wind around the outer periphery of the inner pole D2. In this case, a space may be provided between the portion D1 and the non-reversible magnet 15.

In the above embodiment, the control device 33 receives the induced voltage from the coil 31 via the voltage dividing circuit 32 and warns the alarm device 36 by the program shown in FIG. A warning was sent to the controller 7) of 1A. Alternatively, when the host controller includes a memory and a microprocessor, the program shown in FIG. 4B is set to cause the host controller to detect the induced voltage from the coil 31, and injection molding is performed. The machine 1 may be stopped, or the magnetic clamping device 10 may be remagnetized after being demagnetized once. Also, at this time, the content of the warning may be displayed on the liquid crystal screen of the host controller.

Reference Signs List 1 injection molding machine 2, 3 platen 4, 5 mold auxiliary fitting 8 ejector rod 9 guide rod 10, 20 magnetic clamp device 11, 21 magnet block 12, 22 proximity sensor 13 through hole 14, 24 groove 15 non-reversible magnet 16 Alnico magnet 17 coil (magnetizing coil)
18 reversible magnet 19 yoke 20 magnetic clamping device 31 coil (sensor coil)
32 voltage dividing circuit 33 control device 34 memory 35 table 36 alarm

Claims (5)

A plurality of reversible magnets whose polarities can be reversed and non-reversible magnets provided with an inner pole on the inner circumference side on the surface of a plate made of a magnetic material that magnetically clamps the mold in a magnetized state. In a magnetic clamping device in which a large number of magnet blocks are arranged,
a coil wound around the reversible magnet or wound around the inner pole to detect transient changes in magnetic flux passing through the reversible magnet; and an induction detected from the coil by the transient changes in magnetic flux. Whether or not the positive and negative polarities of the voltage are reversed is determined by a threshold value of the positive and negative voltages, and when the reversal of the positive and negative polarities of the induced voltage is detected, it is possible to determine that the mold has not moved from the initial position. A magnetic clamping device , characterized in that it has a control device for judging that it is in a slightly detached state in which the attracting force is lowered.
2. A magnetic clamping device according to claim 1, wherein said control device judges that the clamping state of the mold including its position has changed when the induced voltage detected from said coil is only negative. and a magnetic clamping device.
2. The magnetic clamping device according to claim 1, wherein when the induced voltage detected from the coil is reversed in polarity, the control device obtains the magnetic flux lost from the induced voltage, A magnetic clamping device characterized in that a magnetic clamping device is characterized in that when a predetermined threshold value is reached by accumulating a lost magnetic flux obtained at times, a warning is issued to prompt re-magnetization of the magnetic clamping device.
In an injection molding machine in which a plate made of a magnetic material is attached to each of the left and right platens, and a mold is clamped to each of the plates,
The mold is magnetically clamped in a plurality of magnetized states having a reversible magnet that is arranged on the surface of each plate and that can reverse the polarity and a non-reversible magnet that has an inner pole on the inner peripheral side. magnet block,
a coil wound around the reversible magnet or wound around the outer circumference of the inner pole for detecting changes in magnetic flux passing through the reversible magnet;
It is determined whether or not the polarity of the induced voltage detected from the coil is reversed due to the change in the magnetic flux, and when the polarity reversal is detected, the mold is in a state where it can be determined that the mold has not moved from the initial position. a control device that determines that the suction force is slightly detached and that the suction force is slightly detached ;
When the control device determines that the mold has not moved from its initial position and is in a state where the adsorption force is slightly detached , the molds clamped on the plates are moved to each other. An injection molding machine characterized by re-magnetizing in a combined state.
In an injection molding machine in which a plate made of a magnetic material is attached to each of the left and right platens, and a mold is clamped to each of the plates,
Each plate has a reversible magnet whose polarity can be reversed and a non-reversible magnet having an inner pole on the inner peripheral side, which are arranged on the surface of each plate, and magnetically clamp the mold when in a magnetized state. a plurality of magnetic blocks;
a coil wound around the reversible magnet or wound around the outer circumference of the inner pole for detecting changes in magnetic flux passing through the reversible magnet;
It is determined whether or not the polarity of the induced voltage detected from the coil is reversed due to the change in the magnetic flux, and when the polarity reversal is detected, the mold is in a state where it can be determined that the mold has not moved from the initial position. and a controller for re-magnetizing the molds clamped on the plates in a state where the molds clamped on the plates are aligned with each other.

Images